(a) The Field of the Invention
This invention is concerned with the art of producing light reflective systems particularly adapted for being utilized in highway marking signs and advertising signs to provide a distinguishing surface and capable of reflecting light from sources as headlight beams, for ensuring visibility at a distance in nighttime. The term retroreflection is hereinafter used to designate a reflective means, element or system which will reflect an incident beam or ray of light in such a manner that a brilliant beam, generally a cone of light, is returned to the source of light even though the incident light strikes the surface of the retroreflective system at an angle.
The invention is particularly concerned with retroreflective systems of the class described in my prior Pat. No. 3,981,557 of the U.S., issued on Sept. 21, 1976.
(B) The Prior Art
The pertinent prior art of this invention is throughoutly described and defined in the above my U.S. Pat. No. 3,981,557, the entire disclosure of which is herein referred to and forms part of this specification, including the several details concerned with the materials, the ranges of index of refraction, the combination and the arrangement of the various components and the modes for making use and taking advantages of said retroreflective systems.
As far as this improvement is specifically concerned, attention can be paid to the illustration of FIG. 2, of my above prior U.S. Patent. There is shown how an incident light beam (which actually forms an angles smaller than that illustrated in said FIG. 2 with the sign surface indicated at S) is retroreflected by one or more reflectorized bead or microsphere such as indicated at 12, located close to said surface S. Taking into in consideration that the light to be retroreflected is the "grazing light", the part of interest of the microspheres is that located in the zone adjacent to the plane defined by said surface, that is the zone which can properly be termed as the "equatorial zone" of the primary focusing transparent body, generally indicated at 10 and having its unique elliptical or nearly elliptical configuration in its sections taken in planes perpendicular to the said sign surface, as claimed.
As shown in FIG. 1 of said prior Patent, the retroreflective composite element is produced, by applying the prior art, as comprising the said primary transparent body and a monolayer of microspheres which completely covers the surface of said body.
As a matter of fact, the beads or microspheres which coat the upper half of said surface (when the system is in service, FIG. 2) must be removed, and therefore wasted, and those which coat the lower portion of the lower half of same surface (where generally a light beam to be reflected will be never focused) are simply useless for the desired retroreflection. Generally speaking, it might be assumed that not more that twenty percent about of the microspheres is actually useful for retroreflection, out from those existing in the manufactured arrangement.